Senate Majority Leader Mitch McConnell on Monday night abruptly called for a vote to repeal Obamacare without an immediate replacement after the latest Republican effort to overhaul the U.S. health-care system fizzled out.

"Regretfully, it's now apparent that the effort to repeal and immediately replace the failure of Obamacare will not be successful," McConnell said in a statement. "So, in the coming days, the Senate will vote to take up the House bill with the first amendment in order being what a majority of the Senate has already supported in 2015 and that was vetoed by then-President Obama: a repeal of Obamacare with a two-year delay to provide for a stable transition period to a patient-centered health care system that gives Americans access to quality, affordable care."

President Donald Trump, who had pressed for a repeal and replacement plan, urged Republican lawmakers to repeal Obamacare first, and then come up with a solution for replacing it. It is unclear if the GOP has the votes to repeal the law without an immediate replacement, as it risks destabilizing insurance markets.

It was the latest setback to the GOP's effort to repeal and replace Obamacare, a Republican campaign promise for most of the last decade that has stalled multiple times this year amid party divisions. The GOP chose to address the health-care overhaul before it took on tax reform, another key campaign plank, and every setback is seen as delaying the party's broader agenda.

Before Trump's tweet, a White House official said in a statement that "inaction is not an option. We look forward to Congress continuing to work toward a bill the President can sign to end the Obamacare nightmare and restore quality care at affordable prices."

Moving toward a vote on a repeal-only plan would require two of the four GOP senators who said they would vote "no" on the motion to proceed to change their tunes. Additionally, it remains to be seen if several other senators who were undecided on the replacement plan will get behind a repeal-only bill.

The GOP-controlled Congress passed a bill in 2015 to repeal Obamacare without a replacement, though the lawmakers cast their votes knowing that the bill would face a presidential veto from then-President Barack Obama.

The Senate voted by a 52-47 margin to only repeal Obamacare in 2015. Many of the current health-care swing votes supported the bill. GOP Sen. Susan Collins of Maine, a strong opponent of the latest Obamacare replacement bill, voted against it.

In 2015, the nonpartisan Congressional Budget Office estimated that repealing Obamacare would lead to 30 million to 32 million more Americans uninsured.

After the Senate's initial struggles to reach a health-care consensus in June, Trump and Sen. Rand Paul, R-Ky., both publicly floated the prospect of repealing Obamacare without a replacement plan.